Adjustable wire-wound component



June 20, 1967 w. D. KIRKENDALL 3,327,275

' ADJUSTABLE WIRE-WOUND COMPONENT Fil ed Oct. 27, 1964 v v 2 Sheets-Sheet 1 f 69 7/ W////am 0. ///r/re/7aa// INVENTOR.

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ATTORNEY June 20, 1967 Filed Oct. 2'7, 1964 W. D. KIRKENDALL ADJUSTABLE WIRE-WOUND COMPONENT 2 Sheets-Sheet 2 INVENTOR ATTO/FIVL'V I W////a/77 .5. Avvewc/o/l United States Patent 3,327,275 ADJUSTABLE WIRE-WOUND COMPONENT William D. Kirkendall, Dalton, Pa., assignor, by mesne assignments, to Weston Instruments, Inc., Newark, N.J.,

a corporation of Delaware Filed Oct. 27, 1964, Ser. No. 406,712 7 Claims. (Cl. 33%--195) ABSTRACT OF THE DISCLOSURE An adjustable electrical device is provided which includes a coil formed of a plurality of turns of a bare conductor, adjacent turns of the conductor being insulated from one another by an insulating potting compound. The coil and the potting compound are encased in a protective housing having an orifice in one end thereof through which one end of the conductor may be pulled to change a coil parameter.

The potting compound has the inherent properties of that class of potting compounds known to those in the electrical art as silicon rubber potting compounds. The silicon rubber potting compounds are typically characterized by their low resistance to tear and their forming nonadhering coverings for potted, bare conductors. These characteristics of the potting compound permit easy withdrawal of the one end' of the conductor from the housing' as a conductor devoid of any insulation. Hence, the conductor which is pulled through the orifice is bare and a good direct electrical connection may be made to this end of the conductor. Thus, there is no need to resort to the relatively difficult expedient of removing insulation from the withdrawn end of the conductor to effect such a connection.

This invention relates to an adjustable wire-wound component, and, more particularly, to a wire-wound component having electrical parameters which may be adjusted while the component is installed in a circuit and its method of use and manufacture.

It is often desirable to provide a means for adjusting an electrical component such as a wire-w0und resistor so that .its resistance can be adjusted to a precise value while the device is installed in a circuit. In the past such incircuit resistance adjustment was provided by slide-type resistors or more expensive potentiometers. However, the minimum physical size of these devices is limited and further problems-are encountered in the maintenance of proper wiper contact.

It is, therefore, an object of the present invention to provide a new and improved adjustable wire-wound component which may be conveniently adjusted, while in place in a circuit, to a desired precise value.

Another object of the present invention is to provide a new and improved wire-wound electrical component which is conveniently adjustable to vary electrical parameters of the component upon melting of a wire holding substance on the component.

Yet another object of the invention is to provide a new and improved method of manufacturing an adjustable Wire-wound component which may be conveniently adjusted to aprecise value and which adjustment may take place while the component is in place in a circuit.

' With these and other objects in view, the present invention is exemplified by a wire-wound component, its method of use and manufacture, which component is conveniently adjustable to a precise value and which value may be fixed in the component. More particularly, the invention includes a component comprised of bare wire wound in a coil within a ceramic core and impregnated with a rubber substance which fills voids between the turns of wire and between the Wire and the core. Each wire end of the coil is positioned through a hole in an end cap on the core and held in place by solder. Upon melting of the solder, the wire may be pulled from within the ceramic core through the end cap until the amount of wire left within the core is sufiicient to provide an electrical parameter having a precise value. The solder on the end cap is then allowed to cool and the excess wire which has been pulled through the end cap is severed to precisely fix the value of the component.

The method of manufacturing such a component comprises the steps of winding a wire within a core or on a mandrel to form a coil and placing the coil within a protective case. End caps are then placed over each end of the protective case and the wire ends of the coil are extended through openings in the caps. A depressed portion on the caps is then filled with solder which when solidified joins the wire ends of the coil with the end caps. Upon subsequent melting of the solder, the extending Wire ends may be pulled to remove wire from the coil within the case. A complete understanding of this invention may be had by reference to the following detailed description when read in conjunction with the accompanying drawings illustrating embodiments thereof, wherein:

FIG. 1 illustrates a cross-sectional view of a resistor incorporating the present invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 shows another embodiment of a resistor incorporating the present invention;

FIGS. 4-8 are illustrative of the steps of manufacturing the resistor shown in FIG. 1; and

FIG. 9 shows an apparatus for manufacturing a wirewound coil by an alternative method.

For purposes of illustration, the following description of the invention will be directed toward a wirewound resistor component. However, it will be readily appreciated that this invention would equally pertain to any wire-wound component such as an inductive device.

Referring now to FIG. 1, a resistor device is shown comprised of a tubular ceramic core or housing 11 within which is positioned a coil of bare wire having a plurality of turns 12. The coil of wire is secured to the interior wall of the ceramic core 11 bymeans of a potting compound 13 which also separates and electrically insulates each turn of wire forming the coil. The ends of the coil wire form leads 14'and 16 which when extended from the coil provide terminal connections. Flanged end caps 17 are positioned over each end of the ceramic core to form an enclosed housing for the resistor. Openings 18 are formed through the end caps to provide an outlet for terminal wires 14 and 16. Electrically conductive terminal pins 19 are conveniently connected to the end caps and extend outwardly from the caps to provide convenient means for connecting the device to electrical circuit wires.

A meltable electrically conductive substance 21 such as solder is shown filling a depressed portion or well 22 in the end caps to seal the opening 18 in the end caps and to provide an electrical connection between the terminal wires 14 and 16 and the terminal pins 19. This meltable substance or solder 21, when solidified, also holds the terminal wires 14 and 16 fixed to the end caps so that the wires may not be pulled from the resistor housing. An insulating covering 23 is provided over the outside of the ceramic core and end caps. This insulating covering is preferably made of a heat shrinkable tubing such as that sold by Dow Corning under the trademark Silastic 1410. A section of this tubing corresponding to the length of the resistor core is placed over the core. Heat is then applied to the assembly to shrink the tubing over the core and end caps. The resulting outer protective covering along with the solder sealed ends renders the resistor component substantially moisture proof.

The resistor component described above may be adjusted as follows: a portion of the wire from the resistance coil is removed through the solder sealed aperture at either end of the component. To make the adjustment, the solder is melted with a soldering iron until the wire can be pulled through the aperture. When the desired resistance is obtained, the solder is allowed to solidify and the excess wire is trimmed flush with the end cap.

FIG. 3 shows an alternative embodiment of the present invention which comprises a coil of wire upon a mandrel to form a resistor element 33. This resistor element is positioned within a tube 35 which is made of fiber glass or other suitable insulation material. The resistor element is held spaced from the walls of the tube 35 by a spacer 36. End caps 39 and 43 are positioned within each end of the tube 35 to enclose the resistor and thereby form a protective housing. Terminals 42, 44 extend outwardly from the respective end caps 39, 43 to provide connecting means between the resistor and circuit wiring. One end of the wire forming the resistive element is shown connected to end cap 39 to provide an electrical connection between one end of the coil and the terminal 42. The terminal 44 may be similarly connected to the end cap 43. An opening 46 is formed through theother end cap 43. The other end of the wire coil serves as a lead 48 which projects through the opening 46 in end cap 43. A meltable electrically conductive substance 47, such as solder, is used to cover and. seal the opening 46. This substance 47, when solidified, holds the lead wire 48 fixed to the end caps to prevent removal or pulling of the wire from about the mandrel. Conversely, upon melting of the substance 47 the lead wire 48 may be pulled to thereby strip or remove the wire forming the resistive element from the mandrel positioned within the tubular housing. Such withdrawal of wire from the coil will adjust an electrical parameter of the component, such as resistance in this instance, with the adjusted value of the component depending upon the amount of wire removed from the coil. When the component has been adjusted to the desired value in such a manner, the m'eltable substance 47 is allowed to solidify to prevent iiurther removal of wire from the coil and thereby fix the resistance of the device at that desired value. The meltable electrically conductive substance 47 also provides an electrical connection between the wire lead 48 and terminal 44 and seals the component from the effects of moisture.

FIGS. 48 illustrate a method of manufacturing the component shown in FIGS. 1 and 2. This method consists of the following steps: A bare electrically conductive wire 50 is wound in spaced turns about a tubular mandrel 51. The mandrel is longitudinally grooved, as shown in the cross-sectional view of FIG. 4A, and is made of a heat-softenable material such as cellulose acetate. For convenience in handling, low melting point wire 55 may be positioned with-in the mandrel with the ends of the wire extending from the mandrel to facilitate mechanized handling of the mandrel during the winding operation.

The wire-wound tubular mandrel is next inserted within a ceramic tube 52 as shown in FIG. 5. A potting compound 53, such as any suitable silicone rubber compound, is poured between the mandrel and inside surface of the ceramic tube and is then cured. As is well known in the art, the potting compound 53 is characterized as having a relatively low resistance to tear, forms a nonadhering covering for bare wire and permits easy withdrawal of the wire as a bare wire from the compound. The potting compound cures to a consistency which will hold the turns of the coil in place within the ceramic tube but which will permit the wire to be pulled from the compound with little effort. The longitudinal grooves in the mandrel allow the potting compound to flow inside the wire coil thus providing additional support (FIG. 2). The potted assembly shown in FIG. 5 is then placed in an oven at 300 Fahrenheit whereupon the cellulose acetate mandrel 51, upon which the wire is wound is stretched lengthwise which causes a reduction in the mandrel diameter to a diameter smaller than that of the wire coil (FIG. 6). This, in turn, permits the removal of the mandrel from inside the potted assembly. If low melting point wire 55 is positioned within the mandrel, the wire will melt during this shrinking operation.

Next, as shown in FIG. 7, the shrunken man-drel is removed and wire leads 54 are pulled from the potting compound at each end of the coil to provide terminations for the coil. This tubular coil section is next assembled with two metal end caps 56 (FIG. 8), which have longit-udinally extending terminal pins 57. The ends of the wire leads 54 are extended to the outside of the end caps 56 through small holes in the end caps. A recessed portion or well 58 formed in the end caps is then covered with solder to provide an electrical termination between the wire leads 54 of the coil element and the terminal pins 57 extending from the end caps. Finally, a protective covering 59 is shrunk over the completed assembly to insulate the outside diameter of the end caps. This protective covering may also conveniently be marked to indicate the type or size of the component.

It may readily be appreciated that other methods may be utilized to place the wire coil within the ceramic tube. Such an alternative method can be performed by the apparatus shown in FIG. 9. This apparatus includes a tubular mandrel 61 which is shown positioned within the interior of a ceramic core 62- into which a coil of wire 63 is being placed. The tubular mandrel has a geared flange 64 which is arranged to engage a gear 66 connected by a shaft to a motor 67. The mandrel and motor are positioned upon a base member 68 having a rack 69 thereon which engages a pinion gear 71. Pinion gear 71 is connected to a suitable source of power, not shown. A spool of wire 72 is shown positioned upon the mandrel 61 for rotation therewith. An opening 73 is formed in the side of the mandrel and is grommeted to provide an entrance for wire wound upon the spool 72 into the interior of the tubular mandrel. A reservoir 74 supplies a potting compound to the mandrel. The reservoir is connected through a pump 76 to a flexible hose 77 which is attached to the end of the tubular mandrel by means of a swivel connection 78. This reservoir and pump system supplies potting compound to the mandrel for application with the wire from reel 72 into the interior of the ceramic core 62.

In the operation of this apparatus, the mandrel is placed within a ceramic core. The motor 67 is started to rotate the mandrel. The pump 76 is actuated to pump the potting terior of the ceramic core. The wire and potting compound are directed onto the interior surface of the core 62 by means of a transverse exit nozzle 79 which is formed on the end of the mandrel. The spacing between the exit nozzle and the interior wall of the core is such that the wire is laid uniformly about and against the interior of the core and is at the same time impregnated with the potting compound. As the tubular mandrel rotates, it is moved longitudinally through the core by the rack and pinion mechanism 69, 71 until the wire has been laid throughout the full length of the core. The apparatus is then stopped and the wire being applied is severed to complete the operation.

It should be pointed out that other steps in the manufacture of the electrical device shown in FIGS. 4-8 may be adapted to principles of automatic manufacture, which principles are not the subject of, nor set forth in, this application.

While the present invention has been disclosed as relating to a resistor, other wire-wound electrical devices could be constructed in the same manner and embody the features of this invention. Additionally, while particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects and therefore the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. In an adjustable wire-wound device; an electrical element made of bare, electrically conductive wire Wound in spaced turns into a coil; an insulating substance filling the space between the turns of wire of said coil, said insulating substance having a relatively low resistance to tear and forming a nonadhering covering for said wire to permit easy removal of the bare wire from said substance by pulling on said wire; a protective housing positioned about said coil, said coil being supported within said housing by said insulating substance, the ends of the Wire of said coil providing terminal means for said electrical device; and at least one of said wire ends projecting from said housing and held stationary with respect to said housing by a meltable substance.

2. An adjustable electrical device comprising: a tubular core made of electrically nonconductive material, a bare wire wound in multiple turns to form a coil within said core, a nonconductive material disposed between the turns of said coil, said nonconductive material having a relatively low resistance to tear and forming a nonadhering covering for said wire to permit easy withdrawal of the bare wire from said material by pulling on said wire, said coil being supported within said housing by said nonconductive material, terminal caps fitted over the ends of said core, at least one end of the bare Wire forming said coil extending through an opening in one of said terminal caps, and a meltable, electrically conductive material bonding said extending wire to said cap and sealing said opening to form an enclosure.

3. The device set forth in claim 2 wherein both ends of the wire coil extend through openings in respective end caps and are bonded thereto by a meltable electrically conductive material, said openings being sealed closed by said meltable material.

4. The device as claimed in claim 2, wherein the one of said terminal caps has a recessed surface portion which includes the opening which receives said one end of said bare wire, said recessed surface portion serving to constrain the electrically conductive material while the material is in a melted state.

5. An adjustable electrical device comprising a coil formed of a plurality of turns of a bare conductor, said conductor having two ends, a housing enclosing said coil and including at least one end having an orifice therein through which one end of the conductor may be drawn, an insulating material filling the spaces between and positioning adjacent conductor turns, said material having a sufiiciently low resistance to tear and forming a nonadhering covering for said conductor to permit easy withdrawal of said one end of said conductor from said material as a conductor which is bare of insulating material.

6. The device as claimed in claim 5, wherein a meltable, electrically conductive material seals the orifice With the bare conductor therein.

7. The device as claimed in claim 5, wherein the insulating material comprises a silicon rubber potting compound.

References Cited FOREIGN PATENTS 9/ 1896 Germany. 10/1937 Germany.

RICHARD M. WOOD, Primary Examiner.

ANTHONY BARTIS, Examiner. J. G. SMITH, Assistant Examiner. 

5. AN ADJUSTABLE ELECTRICAL DEVICE COMPRISING A COIL FORMED OF PLURALITY OF TURNS OF A BARE CONDUCTOR, SAID CONDUCTOR HAVING TWO ENDS, A HOUSING ENCLOSING SAID COIL AND INCLUDING AT LEAST ONE END HAVING AN ORIFICE THEREIN THROUGH WHICH ONE END OF THE CONDUCTOR MAY BE DRAWN, AN INSULATING MATERIAL FILLING THE SPACES BETWEEN AND POSITIONING ADJACENT CONDUCTOR TURNS, SAID MATERIAL HAVING A SUFFICIENTLY LOW RESISTANCE TO TEAR AND FORMING A NONADHERING COVERING FOR SAID CONDUCTOR TO PERMIT EASY WITHDRAWAL OF SAID ONE END OF SAID CONDUCTOR FROM SAID MATERIAL AS A CONDUCTOR WHICH IS BARE OF INSULATING MATERIAL. 